A known method for demagnetizing objects uses an open magnet circuit with a coil which is flown through with a constant alternating current. The magnet core is applied onto the object and the alternating current is switched on. Thereupon the magnet core is slowly pulled away from the object by hand. The demagnetization procedure is greatly influenced by surrounding conditions and may not be precisely reproduced. The demagnetization is incomplete and not always equally good.
Such a method is described in U.S. Pat. No. 4,384,313 (Steingrover). With this, the frequency of the supply voltage of the coil is moved slowly up to the resonance frequency of the associated oscillation circuit, whereupon the voltage is reduced and thus the amplitude of the alternating field acting on the parts to be demagnetized is reduced. A disadvantage of this method lies in the fact that a lot of time is required for the approach to the resonance frequency. The time required is so large that an efficient demagnetization of objects is not possible with a pass-through method.
With a further known method according to DE 3718936 A1 one operates with a coil tunnel with large electromagnets which are flown through by alternating current. The object is pulled through the coil tunnel with a stationary magnetic field. By way of this the object is firstly increasingly subjected to the magnetic field and then reducingly. The demagnetizing effect is limited. Here the effect is improved by mechanically rotating the electromagnets.
With today's use of materials for mechanical components and the widespread use of sensitive electronic components and circuits, the residual magnetism in objects becomes more of a major problem. The residual magnetism present in the objects becomes a major quality criterion for suppliers. By way of greater technology and material selection one may reduce the cost factor in particular with the manufacture of parts in masses. However one has to reckon with other disturbing factors such as indeed the residual magnetism.